This invention relates to a mechanism for controlling parallelism between a pinch roller and capstan shaft in a tape recorder.
A drive mechanism for causing a magnetic tape to run at a constant speed while being clamped between a pinch roller and capstan shaft is widely applied to, for example, a tape recorder. With a mechanism for driving a magnetic tape at a constant speed, it is necessary that the pinch roller be parallel with the corresponding capstan shaft. The reason is that derangement in the parallelism between said two members causes a magnetic tape clamped therebetween to be displaced either upward or downward from the normal position, giving rise to the stretching of only one side of the magnetic tape to obstruct its constant run. To avoid such difficulties, various mechanism have been provided to control parallelism between the pinch roller and capstan shaft. The pinch roller is generally rotatably supported by a support arm which is fixed to an immovable base board or a movable head lever base board. Parallelism between the pinch roller and capstan shaft is maintained by controlling the inclination of the pinch roller shaft or support arm shaft. According to a known mechanism for controlling parallelism between a pinch roller and capstan shaft disclosed, for example, in Japanese Utility Model Publication No. 37851/73, a pinch roller shaft is rotatably supported between the base board and support arm movably fitted thereto. The support arm is provided with a non-threaded hole into which a screw is loosely inserted. The screw is threadedly engaged with a female screw formed in the base board through the hole, thereby immovably setting the support arm on the base board. When the screw is first loosened to allow for the free movement of the support arm, later parallelism between the pinch roller and capstan shaft is controlled, and the screw is fully engaged with the aforementioned female screw hole, then the support arm is fixedly mounted on the base board with the parallelism fully maintained. This arrangement is simple and facilitates the control of the parallelism. To assure the constant run of a magnetic tape, the pinch roller should generally be pressed against the capstan shaft with a certain magnitude of urging force. With the above-mentioned arrangement, however, the support arm is fixed to the base board, making it impossible to adopt the known process of pressing the support arm against the capstan shaft, and presenting difficulties in applying a constant urging force to the support arm. Moreover, the known mechanism for controlling parallelism between the pinch roller and capstan shaft objectionably demands a large space.